Printer bar and magnet structure



F. PAGE, JR

PRINTER BAR AND MAGNET STRUCTURE Sept. 29, 1959 2 Sheets-Sheet 1 Filed Sept. 16, 1955 INVENTOR.

F. PAGE, JR

PRINTER BAR AND MAGNET STRUCTURE Filed Sept. 16, 1955' 2 Sheets-Sheet 2 m -Vv' I 6 m rm 5 N .N m M m m by a motor (not shown).

States Patent PRINTER BAR AND MAGNET STRUCTURE Franklin Page, In, Arcadia, Calif., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application September 16, 1955, Serial No. 534,897

10 Claims. (Cl. 346-74) This invention relates to printing apparatus and more particularly to a magnetically operated printer bar assembly.

The present invention, which may be used, for example, in the recording receiver of facsimile equipment, comprises an elongated C-shaped magnet mounted closely adjacent a rotary drum. A movable hollow printer bar encircling one arm of the magnet and extending through the gap thereof has an integral marking edge positioned to effect the printing operation, in cooperation with the drum, upon a marking medium looat'ed between the printer bar and the drum. Movement of the printer bar and its marking edge is effected by energization of a coil mounted within and extending through the hollow printer bar.

It is an object of this invention to provide an improved printer bar and magnet structure.

A further object of this invention is the provision of a printer bar assembly having a high available response frequency.

Another object of the invention is to provide a printer bar structure which requires a minimum of driving power.

Still another object of the invention is the provision of a printing apparatus which utilizes a magnetic braking effect for elimination of jitter.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Figpl is an elevation view of one end of the printer head and drum;

Fig. 2 is a pictorial view, with parts broken away, of the printer head;

'Fig. 3 is a section through the printer head; I Fig. 4 is a section showing details of the printer head; 1 Fig. 5 is a pictorial view of the printer bar; and Fig. 6 is an enlarged section taken on lines 66 of Fig. 5.

Rotatably mounted upon a suitable support 10 is a drum 12 having a conventional helix wire (not shown) secured to the non-magnetic, electrically conductive periphery thereof as is well known. A printing medium 1 4 which may comprise superimposed carbon and white paper sheets is unwound from paper roll 16 and drawn over the helix wire of the drum when the latter is driven I I An elongated C-shaped magnet 18 having a pair of arm portions defining a pole forming gap 20 is secured at the ends thereof in recess es formed in a'pair of spaced mounting units 22, 24 which are pivoted to support 10 at 26 and rigidly interconnected by tie bars 28. A pair of pivoted latches 30 releasably secure the mounting units in the operative position shown in Fig. 1 with the magnet located closely adjacent the peripheral surface of the drum. The distance between drum and magnet is selectively determined by abutment of stop 32 carried by support 10 with a detachable and replaceable stop and shim assembly 34 carried by units 22, 24.

Completely encircling one of the arm portions of the magnet and extending through the gap thereof is an endless hollow or tubular printer bar structure 36 having an integral marking edge 38 and carrying the driving coil 40 entirely confined therein. As best shown in Figs. 5 and 6, the printer bar is a substantially box section beam of endless rectangular loop configuration. A pair of rigid rails 42, 44 are bent in similar rectangular loops and fixedly secured to each other in spaced relation by an inner cover sheet 46. Rail 44 is shaped to provide an integral striking edge 38 for substantially that portion of its length which extends through the magnet gap. Driving coil 40 is wound about inner cover sheet 46 between the rails and the outer cover sheet 48 is secured to the outer surfaces of the rails to provide a rigid but light weight box beam. The beam is immersed in a liquid resin, which penetrates the beam through holes 47 in sheets 46, 48, provided for this purpose, and successively subjected to low pressure, high pressure and heat whereby the resin solidifies and the coil is securely mounted within the tubular beam. Rails 42, 44 are non-magnetic material such as fully austenitic stainless steel or the like having a high modulus of elasticity. The sides or cover sheets 46, 48 may also be of stainless steel for ease in spot welding. However, nonmagnetic properties are not necessary in these sides since a magnetic material merely has the effect of reducing the effective magnetic gap length of magnet 18.

The rectangular loop formed by the metallic printer bar structure 36 is made electrically discontinuous to prevent action thereof as a shorted-turn-shunt on the driving coil. All metallic components are made slightly shorter than the circumference of the coil to provide an insulating space through which extend the coil leads. To complete the mechanical structure of the looped beam, a pair of non-conductive splices 50, 52 are suitably secured thereto by cement, clamping strips or the like to bridge the insulating space.

The printer bar structure is hingedly connected with the magnet by a pair of thin metallic strips 53, each having one end thereof fixed to a portion of the bar 36 external to the magnet gap and the other end thereof fixed to a fixed portion of the printer head. This arrangement eliminates lost motion of a pivot while providing only a very light restraint upon the coil. This suspension has a relatively low natural frequency and a small amount of damping is required to eliminate bounce at this frequency. There is provided for this purpose a thermostatically controlled viscous damping device (Fig. 3) which comprises a pair of movable pistons 54 and fixed oil film cylinders 56. Actual damping depends on viscous fluid film damping between piston and cylinder walls. Piston rods 58 extend through apertures in the bight of the magnet and rigidly interconnect through alignment washers the pistons 54 with that portion of the printer bar structure within the magnetic gap. As the viscous damping film within the cylinder thickens appreciably at the low temperatures to which the apparatus may be subjected, there is wound about each cylinder a heater coil 60 which is controlled by thermostats 62 set to make and break the heater circuits at intermediate temperatures such as 60 and 70 F. The

cylinders, thermostats, and terminal assembly 64 therespectively abut the edges of the printer bar to limit mo- 3 tion thereof to a distance which may be on the order of 0.0015 inch. Rotation of screws 68 shifts both stops thereof simultaneously whereby contact pressure of the printer bar may be adjusted and maintained by lock nuts 74.

The driving coil within the hollow center of the printer bar may have a center tapped winding each half of which is in the plate circuit of suitable driver tubes (not shown). When the black tubes conduct, the white tubes are cut off and vice-versa. The interaction of the field produced by the current in the driving coil and the field of magnet 18 creates a motor force in the winding and the printer bar which is secured thereto. During a black signal this motor force drives the printer bar toward the rotating drum to press the marker edge 38 against that portion of the helix wire intersecting the line of the marker edge whereby the carbon paper is forced against and marks the white paper. During a white signal the printor bar is driven from the drum whereby there is reduced pressure on the paper and there is no marking.

The disclosed printer bar is an exceedingly rigid structure for its weight and has a high natural frequency, thus avoiding the vibration which would yield false marking in the center of the marking edge and raising the upper frequency limits. This high natural frequency in conjunction with the direct linkage between coil and marking edge permits the desired high frequency response with minimum signal power in the coil circuit.

All facsimile equipment needs maximum available damping for jitter elimination. This is usually in the form of some sort of a brake. This brake provides a steady load on the transmitter or receiver drum and by loading all gears, pins, keys and couplings reduces to a minimum the eifect of the clearances necessarily present in all such'devices.

'The brake should also be selected to cause the synchronous motor to operate on that portion of its characteristic curve where it is least sensitive to load variations. With all synchronous motors the phase shift (lag of mechanical rotation behind the rotation of the electrical field) is dependent upon the load applied to the motor shaft. If this load varies, the motor phase shift varies, producing jitter in the copy. The brake causes the motor load to be more uniform than it would be without such a brake, thus reducing jitter caused by phase shift variations.

Mechanical friction brakes are usually used for this purpose. Unless extremely accurately made and running on a smooth, true surface, they tend to introduce load variations of their own. As the brake surface wears and as its temperature changes, its characteristics change; sometimes unfavorably.

In the present invention the braking effect is provided by the proximity (about 0.04 inch) of the drum and gap of the magnet. The movement of the non-magnetic, metallic drum surface in the field of magnet sets up induced currents in the drum to produce a retarding force thereon. This braking force has been found to be so 4 the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A printing apparatus comprising a printing bar, a magnet having a gap therein, a fiat hollow beam of loop configuration, a coil having at least a portion thereof within said barn and mounted for movement in said gap, and marking means secured to an edge of said beam.

2. A printing apparatus comprising a printing bar, a magnet having a gap therein, a pair of rails of loopconfiguration, means for fixedly securing said rails to each other such that an inner edge of one rail is in spaced relation to an inner edge of the other rail, and a coil mounted between inner spaced edges of said rails and positioned for movement in said gap, one of said rails having marking means formed integrally with an outer edge thereof.

3. A printing apparatus comprising a printing bar, a magnet having a gap therein, a pair of inner edge rails each forminga loop of similar configuration, cover means secured to inner and outer surfaces of said rails to form therewith a hollow beam of loop configuration, one of said rails having an integral marking outer edge, and a coil within said hollow beam positioned between said rails and mounted for movement in said gap.

4. The structure of claim 3 wherein said magnet has at least a portion thereof extending within the loop of said beam, and means for swingably mounting said beam for said movement relative to said magnet.

5. In a device of the class described, a magnet having a gap therein,- a tubular fiat printer bar comprising a pair of inner edge spaced rails of loop configuration and hav ing at least a portion thereof disposed within said gap, means for mounting said bar for movement of said bar portion relative to said magnet, a coil mounted within said tubular bar between said rails, and marking means on an outer edge of one of said rails.

6, A printer bar and magnet assembly comprising a C-shaped magnet having a pair of arm portions forming a gap therebetween, a 'hollow printer bar comprising a pair of inner edge spaced rails of loop configuration extending about one of said arm portions and through said gap, means mounting said bar for movement thereof in said gap, at least that portion of said barextending through said gap having a striking edge integrally formed on an outer edge of one of said rails, and a coil wound within said hollow bar positioned between said rails.

7. A printer bar and magnet assembly comprising a fixed elongated magnet of C-shape in cross-section, said magnet having a pair of arm portions forming an elongated gap therebetween, a rigid, hollow substantially rectangular printer bar encircling one of said arm portions and extending through said gap, said bar comprising a pair of spaced rectangular non-magnetic rails, a pair of great that movement of the magnet about 0.01 inch from I its normal position toward the drum is sumcient to cause the synchronous drum driving motor to drop out of synchronism.

Thismagnetic braking has no starting friction and is approximately proportional to drum speed. It is not sensitive to manufacturing irregularities and precise alignment and fine finishes are not required. There is no wear and little sensitivity of environmental changes. The braking action can be easily adjusted to obtain optimum damping constant by changing the thickness of the shims in assembly 34 to vary the distance between drum and magnet. Major changes may be effected by changing the drum material to a material of different electrical conductivity.

Obviously many modifications and variations of the present invention are possible in the light of the above; teachings. It is therefore to be under tood cover sheets fixedly connecting inner and outer surfaces of said rails to form therewith said hollow bar, that rail further from the magnet center being integrally formed with a striker edge, a coil wound within said printer bar between said sheets and rails, a pair of flexible strap members each having one end thereof fixed to a bar portion external to said 'gap, means for fixing the other ends of said strap members relative to said magnet, and means for energizing said coil to cause said printer bar and its striker edge to swing on said strap members relative to said magnet. I V

8. The assembly of claim 7 including thermostatically controlled viscous damping means secured to said printer bar.

9. A printing apparatus comprising a G-shaped magnet having a pair of arm portions forming a gap therebetween, :an electrically conductive non-magnetic drum mounted for rotation closely adjacent said gap, a flat printer bar mounted for movement in said gap toward and from said drum, said bar comprising a rigid beam of hollow crosssectipn having a pair of inner edge spaced rails of' loop i, configuration and an integral marking edge formed on the outer edge of one of said rails facing said drum, a coil mounted between said rails having at least a portion of the windings thereof extending through said hollow beam, and means for energizing said coil to cause said bar to move toward and from said drum.

10. The apparatus of claim 9 including adjustable means for limiting the movement of said printer bar, and means for varying the spacing between said magnet and drum.

References Cited in the file of this patent UNITED STATES PATENTS Kleinschmidt July 7, 1936 Peek June 17, 1941 Turner June 22, 1943 Young et a1 Nov. 9, 1954 

